Minecraft lags with my GTX 970

It's probably your Java version creating the problem. Make sure your running the appropriate version for the mod pack you are playing. Try older and newer versions too because some Java versions cause MC to run worse even though it may be a newer version.
 
Are you using GeForce experience optimized settings? Sometimes that program will bump up resolution into dsp, or in other words it'll bump resolution to like 2k, render the picture, then downgrade back to 1080p, makes for a cleaner picture, but can cause problems. Also check v-sync settings, having a gpu that powerful capped at 60fps, while pushing 300fps+ can be problematic